Turn screws (i.e. screwdrivers for daily use) are extensively used to assembling and disassembling various work pieces. Currently combination screwdrivers are available to meet the need for assembling and disassembling work pieces of different style/sizes. Combination screwdrivers may be roughly divided into two categories.
The first category includes tips and shafts that are removable from handles. The bits or shafts and handles are stored separately. Different screwdrivers may be formed by changing bits or shafts. This category of combination screwdrivers are suitable for a wide range of applications and are practical. However, bits or shafts that are not in use need specific space for storage, thus requiring extra space and inconvenient to carry around and use. Additionally, bits or shafts may be easily lost when not properly stored.
The second category includes built-in storage. Different screwdrivers may be formed by switching the tip or shaft using a mechanical structure or other means. This category of combination screwdrivers require small storage space, and easy to carry. Bits or shafts that are switched off are not easily lost. However storing multiple bits or shafts together usually results in complex inner structures and makes it inconvenient to change bits or shafts.
For example, Chinese invention patent application serial No. 200910049964.4 discloses a unitary combination screwdriver. FIG. 1 illustrates the structure of one embodiment of the unitary combination screwdriver. The body of the screwdriver is assembled from a cylindrical plastic handle sleeve 25, a hexagonal metal shaft sleeve 24, a metal clamp head 23, and a plastic protective cover 22 for protecting screwdriver bits 21. The threaded clamp head 23 is magnetic. The handle is hollow and is formed to a standard size so that various types of screwdriver bits 21 can be stacked and inserted inside the screwdriver. This type of unitary combination screwdriver overcomes the disadvantages of ordinary combination screwdrivers, i.e. separate storage for screwdriver body and screwdriver bits, thus effectively reducing the overall volume of the screwdriver. The unitary combination screwdrivers match different types of screws by simply changing the order of the embedded screwdriver bits. However, it is inconvenient to change screwdriver bits since the screwdriver bits 21 are stored inside the shaft sleeve 24 in a stacked manner. For example, to use the screwdriver bit that is stored in the back of the shaft sleeve 24, it is necessary to remove the multiple screwdriver bits positioned over the needed screwdriver bit. The operation is complicated and severely reduces operating efficiency.
For example, Chinese utility model patent No. 201020185037.3 discloses an automatic bit-changing screwdriver, which includes an outer shield, an inner shield, a shaft, a shaft guiding base, a plurality of guiding shaft elements and a bit guiding sleeve. The inner shield and outer shield are slidingly coupled to each other. The shaft is disposed inside the inner shield and the outer shield. The shaft is fixedly connected to the outer shield to push or pull the bit. The shaft has a sloped surface. A shaft leading magnet is disposed on a front end of the shaft. The shaft guiding base is disposed between the inner shield and the shaft and fixedly attached to a back end of the inner shield. The plurality of guide shaft elements are connected along a periphery of the shaft guiding base and rotationally coupled to the shaft guiding base. Each guiding shaft element has a convex arc surface corresponding to a perspective position on the sloped surface. However the multiple bits of the screwdriver result in a complicated inner structure. Further because all the bits are disposed in the bit guiding sleeve, a needed bit cannot be obtained by one pump.
In conclusion, the state of the art combination screwdrivers are generally inconvenient for bit-changing and usually require operators to touch the bits by hand during bit-changing, thus, causing contamination, erosion and rust.